It is known in the art to which this invention pertains that acid zinc baths are characterized by very high anode and cathode efficiencies and also by low anode and cathode polarizations. These properties, however, result in a throwing power of the bath which is relatively poor. Accordingly, acid zinc electroplating baths generally are limited to the plating of relatively simple shapes or to the employment of special and relatively elaborate anode arrangements or complicated racking facilities in order that good metal distribution can be obtained.
The expression employed herein, namely "throwing power" refers to the ability of the acid zinc plating solution to deposit metal uniformly upon an irregularly shaped cathode. In order to measure throwing power in a typical test, a J-shaped electrode is suspended in the plating bath as the cathode between a pair of vertically disposed and generally rectangular anodes. The thickness of the zinc deposited in the deepest recesses of the cathode is then expressed as a percentage of the thickness of the zinc deposited on that portion of the cathode relatively closer to the anode and fully exposed to the anode.